1. Field of the Invention
The present invention relates to a steering damper apparatus for use on a small vehicle such as a motorcycle, and to a vehicle incorporating the novel steering damper.
2. Background Art
In a motorcycle, steering is performed by operating a handlebarbar to pivotally turn a steering stem, pivotally inserted into a head pipe at the front end of a vehicle body frame, where the steering stem is connected to a front fork, which supports a front wheel. Such a motorcycle may be provided with a steering damper apparatus located between the steering-side member, which rotates when the handlebar is operated, and the vehicle-body-side member which does not rotate, when the handlebar is operated.
In such a steering damper arrangement, the steering damper apparatus is only required to generate a small damping moment during normal travel, in which the turned angle of the handlebar is small and the angular speed is low. Conversely, the steering damper apparatus is required to generate a high damping moment where the turned angle of the handlebar is large and the angular speed is high. It would be advantageous to restrain a burden of the handlebar operation as much as possible by setting the damping moment in the low-speed range to a small value in a situation in which the speed is low and small turns occur continuously.
Therefore, in the steering damper art, there is a known steering damper apparatus for a motorcycle in which the above-described requirements are satisfied by using a swing-type damper, and providing a bypass for varying a damping force in a complex manner.
However, the steering damper apparatus employing such a swing-type damper is complex in structure and expensive, and in addition, bulky and heavy. Therefore, it may constrain the arrangement of other parts.
There is also another known steering damper apparatus for a motorcycle which is configured by a cylindrical damper which has a simple structure and is inexpensive, which has been well known for a number of years (For example, see Japanese Published Patent Document JP-UM-B-64-4633). The steering damper apparatus disclosed by this reference includes a cylindrical damper having a damper case and a damper rod sliding in the damper case, in which the damper case is pivotally connected to a head pipe on the vehicle body side, and to a first fork bridge on the steering side. Also in the steering damper in the reference, the damper rod is pivotally connected to another one of the fork bridges on the steering side. In such a case, a connecting point on the fork bridge side is a position closer to either one of left and right ends of the fork bridge.
According to the steering damper apparatus as described above, since the cylindrical damper is contracted when the handlebar is turned to the right, and expanded when turned to the left, a damping effect may be generated on either sides. Accordingly, the damping force can be generated at the limits of rotation.
Generally, the cylindrical damper design generates a uniform damping force in a contracting stroke or an expansion stroke of the damper. Therefore, the apparatus configured such that the cylindrical damper is contracted on one side and expanded on the other side depending on the turning direction of the handlebar, as stated in JP-UM-B-64-4633 may have the same characteristics when the handlebar is turned in either directions of right or left from the steered angle of zero degrees, but it is difficult to configure the apparatus so as to generate different values of the damping force when the handlebar is turned from the steered angle of zero degrees when the handlebar is turned to the steered angle of zero degrees. It is also difficult to provide an angle-dependent characteristic to the steered angle of the handlebar. Furthermore, in the apparatus stated in JP-UM-B-64-4633, a long damper stroke is structurally required, and hence a compact layout cannot be achieved.